1. Field of the Invention
This application relates generally to low dielectric constant polymer materials and more particularly to solvent systems for use with arylene ether based polymer materials.
2. Description of the Related Art
As the dimension of the interconnect design rules for integrated circuits (IC) undergoes progressive shrinkage to sub-quarter micron metal spacing, the use of organic polymer dielectrics to minimize capacitance and reduce power consumption and cross talk, while increasing signal propagation speed becomes a necessity. The organic dielectrics must possess dielectric constants no higher than 3.0 and should have dielectric constants as low as possible toward a theoretical limit of 1.0. The practical expectation for polymer dielectrics is in the range of 2.2 to 3.0. The organic dielectrics must have glass transition temperatures above 300.degree. C. and as high as possible toward 450.degree. C., a value determined by the thermal stability of organic polymers. The organic dielectrics should also be easily processed, preferably, by standard spin-bake-cure processing techniques. The organic dielectrics should also be free from moisture and out-gassing problems, in addition to having expected adhesive and gap-filling qualities, and dimensional stability towards thermal cycling, etching, and chemical mechanical polishing processes.
Arylene ether polymers, such as poly(arylene ether) (PAE), poly(arylene ether ether ketone) (PAEEK), poly(arylene ether ether acetylene) (PAEEA), poly(arylene ether ether acetylene ether ether ketone) (PAEEAEEK), poly(arylene ether ether acetylene ketone) (PAEEAK), and poly(naphthylene ether) (PNE) comprising different polymer designs that include homopolymers, block or random copolymers, polymer blends, interpenetrating polymer networks (IPNs), and semi-interpenetrating polymer networks (SIPNs), are materials that have been identified as organic dielectrics.
Taking advantage of the low dielectric property of these organic materials requires the IC industry to make a significant shift in its processing paradigm. New processing approaches, such as the use of spin-coating, require selection of appropriate solvents for formulation of the spin-on polymer solution, cleaning, edge-bead removal, and wafer backside rinsing. Desirable formulations will provide spin-coated polymer dielectric films with excellent uniformity, a wide thickness range from hundreds of angstroms to hundreds of microns, very low out-gassing at high temperature, excellent gap-filling to 0.1 micron, excellent local, regional and global planarization, and ease of wafer edge bead removal and wafer backside rinsing. In addition, the spin-on dielectric polymer solution should be easily filtered to minimize its manufacturing cost. Finally, the solution must be environmentally acceptable.
While conventional alcoholic solvents media used for spin-on glasses, familiar to IC engineers, are obvious solvent candidates, they cannot necessarily be applied to organic materials. Their environmental benevolence, in many cases, ease in clean up, and low viscosity features are much desired. Ketonyl and other aprotic solvents have been used for photoresists and polymer dielectrics. These solvents include methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, cycloheptanone, cyclooctanone, .gamma.-butyrolactone, N-methylpyrrolidinone, N-cyclohexylpyrrolidinone and N,N-dimethylacetamide. Among them, cyclic ketonyl solvents are commonly used as solvents for arylene ether dielectrics. However, cyclic ketones normally are not as miscible with most arylene ether polymer dielectrics as would be desired and the spin-on solutions formulated from these solvents usually yield some extent of striation on the spin-coated film, especially for films with thicknesses greater than 1.5 micron. Serious striation could cause inadequate gap-filling, problems in adhesion of the dielectric film with a substrate and other problems. Additionally, cyclic ketonyl solvents have varying degrees of moisture, pH, and photosensitivities, often exacerbated by heat. Users need to be cognizant of these potential difficulties. For example, cyclopentanone is significantly more sensitive than first thought toward low pH, in addition to its well-known sensitivity toward light, moisture, and high pH. Cyclohexanone is more stable than cyclopentanone and has been a fair solvent for photoresists in the industry. However, cyclohexanone is still sensitive to light and low pH. Furthermore, cyclohexanone is considered to be barely tolerable by the industry due to its very low exposure limit.
To summarize, as knowledge in the application and processing of organic dielectric materials expands, shortcomings among the currently-used cyclic ketonyl solvents are becoming more recognized. It would be desirable to provide process compatible and benign solvents for arylene ether polymer dielectrics. In particular, it would be desirable to provide a family of extremely useful high-boiling point solvents for formulation of spin-on dielectric polymer solutions, edge bead removal of these dielectric films, and wafer backside and spin-coater rinsing.